Gas substitution control system and method for bi-fuel engine

Abstract

A gas substitution ratio control system varies natural gas flow to a bi-fuel engine based on detected diesel flow to maintain a desired gas substitution ratio (GSR), without any requirement to sense engine load. In other words, GSR is controlled without monitoring engine load level. In one system, an engine is first calibrated to map actual gas and diesel flows to provide the correct GSR for all engine loads. The calibration data is then stored and diesel flow rate is monitored. The current detected diesel flow rate is used to determine the required gas flow rate for correct GSR. Gas flow to the engine is then adjusted to correspond to the required gas flow rate. Other embodiments meter gas to maintain the diesel flow rate at the same minimum level for all loads, or meter gas and diesel fuel flows to match a map of the limiting fuel energy based GSR (gas fuel energy rate/total fuel energy rate) at all loads for each engine model.

We claim: 
     
         1 . A method of controlling gas substitution ratio in a bi-fuel engine, comprising:
 calibrating a bi-fuel engine having a gaseous fuel input and a non-gaseous fuel input over a range of engine loads to determine the gaseous fuel flow and corresponding non-gaseous fuel flow to produce predetermined gas substitution ratios (GSR) over the calibrated load range;   storing the calibration data in a data base;   detecting current non-gaseous fuel flow to the engine;   using the stored calibration data to determine the gaseous fuel flow corresponding to the current detected non-gaseous fuel flow;   controlling a gas metering assembly to produce a gaseous fuel flow to the engine corresponding to the determined gaseous fuel flow computed from the stored calibration data; and   continuing to monitor the current non-gaseous fuel flow to the engine and adjusting the gaseous fuel flow in response to variations in detected non-gaseous fuel flow in order to maintain the GSR at or close to the predetermined level and compensate for variations in detected non-gaseous fuel flow.   
     
     
         2 . The method of  claim 1 , wherein the non-gaseous fuel is diesel (DF) and the gaseous fuel is natural gas (NG). 
     
     
         3 . The method of  claim 1 , wherein the non-gaseous fuel is diesel (DF) and the gaseous fuel is propane. 
     
     
         4 . The method of  claim 1 , wherein gaseous fuel flow to the engine is adjusted by controlling the gaseous fuel pressure to the engine. 
     
     
         5 . The method of  claim 1 , further comprising detecting increase in acceleration of the engine and determining a gas flow bias based on the detected increase in acceleration, and controlling the gas metering assembly to reduce the gaseous fuel flow by the determined gas flow bias. 
     
     
         6 . The method of  claim 1 , wherein the step of detecting non-gaseous fuel flow to the engine comprises detecting a supply flow A of non-gaseous fuel to a non-gaseous fuel injector, detecting a return flow B of non-gaseous fuel from the injector, and determining non-gaseous fuel flow to the engine by subtracting return flow B from supply flow A. 
     
     
         7 . The method of  claim 6 , wherein the method of detecting supply flow A of non-gaseous fuel to a non-gaseous fuel injector and the method of detecting a return flow B of non-gaseous fuel from the injector are at predetermined speeds sufficient to measure the flow for each injector. 
     
     
         8 . The method of  claim 1 , wherein the step of detecting non-gaseous fuel flow to the engine comprises reading the fuel flow parameter from the electronic control unit (ECU) of the engine. 
     
     
         9 . A method of controlling gas substitution ratio in a bi-fuel engine, comprising:
 calibrating a bi-fuel engine having a gaseous fuel input and a non-gaseous fuel input by monitoring the non-gaseous fuel input while running the bi-fuel engine at full load and increasing gaseous fuel flow to the bi-fuel engine until an engine misfire is detected;   selecting a minimum non-gaseous fuel flow set point which exceeds the non-gaseous fuel flow corresponding to the engine misfire;   storing the selected minimum non-gaseous fuel flow set point in a data base;   detecting non-gaseous fuel flow rate to the engine during normal operation;   comparing the detected current non-gaseous fuel flow rate to the minimum non-gaseous fuel flow set point;   controlling a gas metering assembly to vary the gaseous fuel flow to the engine until the non-gaseous fuel flow to the engine corresponds to the minimum non-gaseous fuel flow set point; and   continuing to monitor the current non-gaseous fuel flow to the engine and adjusting the gaseous fuel flow rate in response to variations in detected non-gaseous fuel flow from the selected minimum non-gaseous fuel flow set point in order to maintain the non-gaseous fuel flow rate at or close to the selected minimum non-gaseous fuel flow set point.   
     
     
         10 . The method of  claim 9 , wherein the non-gaseous fuel is diesel and the gaseous fuel is natural gas. 
     
     
         11 . The method of  claim 9 , wherein the non-gaseous fuel is diesel (DF) and the gaseous fuel is propane. 
     
     
         12 . The method of  claim 9 , wherein gaseous fuel flow to the engine is adjusted by controlling the gaseous fuel pressure to the engine. 
     
     
         13 . The method of  claim 9 , further comprising detecting increase in acceleration of the engine and determining a gas flow bias based on the detected increase in acceleration, and controlling the gas metering assembly to reduce the gaseous fuel flow by the determined gas flow bias. 
     
     
         14 . The method of  claim 9 , further comprising selecting a predetermined cut off non-gaseous fuel flow set point corresponding to a minimum idle flow setting, and cutting off gaseous fuel flow to the engine when the adjusted gaseous fuel flow output corresponds to a non-gaseous fuel flow rate below the cut off non-gaseous fuel flow set point. 
     
     
         15 . The method of  claim 14 , wherein the predetermined cut off non-gaseous fuel flow set point is between minimum idle flow and the selected minimum non-gaseous fuel flow set point. 
     
     
         16 . The method of  claim 9 , wherein the step of detecting non-gaseous fuel flow to the engine comprises detecting a supply flow A of non-gaseous fuel to a non-gaseous fuel injector, detecting a return flow B of non-gaseous fuel from the injector, and determining non-gaseous fuel flow to the engine by subtracting return flow B from supply flow A. 
     
     
         17 . The method of  claim 9 , wherein the step of detecting non-gaseous fuel flow to the engine comprises reading the fuel flow parameter from the engine's electronic control unit (ECU). 
     
     
         18 . A method of controlling gas substitution ratio in a bi-fuel engine, comprising:
 calibrating a bi-fuel engine having a gaseous fuel input and a non-gaseous fuel input at different loads to determine the gaseous fuel flow and corresponding non-gaseous fuel flow at varying engine loads to calibrate a command gaseous fuel substitution ratio (GSR) based on fuel energy at varying engine loads for the bi-fuel engine;   mapping total fuel energy rate (gas fuel energy rate/total fuel energy rate) against the calibrated GSR to create GSR mapping data;   storing the GSR mapping data in a data base;   detecting current gaseous fuel flow rate and non-gaseous fuel flow rate to the engine;   determining the fuel energy rate corresponding to the current detected gaseous and non-gaseous fuel flow rates;   using the stored GSR mapping data to determine a command GSR corresponding to the currently detected gaseous and non-gaseous fuel flow rate;   determining the actual GSR from the currently detected gaseous and non-gaseous fuel flow rates;   comparing the current GSR to the command GSR; and   varying the gas flow to the engine in response to detected differences between the current GSR and the command GSR to adjust the actual GSR to be at or close to the desired command GSR.   
     
     
         19 . The method of  claim 18 , wherein the non-gaseous fuel is diesel and the gaseous fuel is natural gas. 
     
     
         20 . The method of  claim 18 , wherein the non-gaseous fuel is diesel (DF) and the gaseous fuel is propane. 
     
     
         21 . The method of  claim 18 , wherein gaseous fuel flow to the engine is adjusted by controlling the gaseous fuel pressure to the engine. 
     
     
         22 . The method of  claim 18 , further comprising detecting increase in acceleration of the engine and determining a gas flow bias based on the detected increase in acceleration, and controlling the gas metering assembly to reduce the gaseous fuel flow by the determined gas flow bias. 
     
     
         23 . The method of  claim 18 , wherein the step of detecting non-gaseous fuel flow to the engine comprises detecting a supply flow A of non-gaseous fuel to a non-gaseous fuel injector, detecting a return flow B of non-gaseous fuel from the injector, and determining non-gaseous fuel flow to the engine by subtracting return flow B from supply flow A. 
     
     
         24 . The method of  claim 18 , wherein the step of detecting non-gaseous fuel flow to the engine comprises reading the fuel flow parameter from the engine's electronic control unit (ECU). 
     
     
         25 . A gas substitution control system for a bi-fuel engine having a gaseous and a non-gaseous fuel input, comprising:
 a gaseous fuel input assembly connected to a gaseous fuel input of a bi-fuel engine and a non-gaseous fuel injector assembly connected to a non-gaseous fuel input of the bi-fuel engine;   a non-gaseous fuel flow detector module configured to detect non-gaseous fuel flow to the engine and produce a non-gaseous fuel flow output;   a gaseous fuel flow control module communicating with the non-gaseous fuel flow output of the non-gaseous fuel flow detector module and configured to vary gaseous fuel flow to the engine based on at least a current non-gaseous fuel flow output of the non-gaseous fuel flow detector module.   
     
     
         26 . The gas substitution control system of  claim 25 , wherein the gaseous fuel flow control module further comprises a data storage unit having stored calibration data for the bi-fuel engine, and the gaseous fuel control module is programmed to vary gaseous fuel flow to the engine based on the stored calibration data in addition to the detected current non-gaseous fuel flow to the engine. 
     
     
         27 . The gas substitution control system of  claim 26 , wherein the stored calibration data comprises a range of non-gaseous fuel flow rates and corresponding gaseous fuel flow rates providing predetermined gas substitution ratios (GSR) of gaseous fuel flow to total gaseous and non-gaseous fuel flows over a range of engine loads, and the gaseous fuel flow control module is configured to look up the calibrated gaseous fuel flow rate corresponding to the current detected non-gaseous fuel flow rate in the stored calibration data and to adjust the gaseous fuel flow rate based on the stored gaseous fuel flow rate corresponding to the detected non-gaseous fuel flow rate. 
     
     
         28 . The gas substitution control system of  claim 27 , further comprising an acceleration detection module configured to detect acceleration of the engine as a result of decreased engine load and to produce an acceleration output signal, a gaseous fuel flow bias module having an input which receives the acceleration output signal and produces an output comprising a gas flow bias amount dependent on the acceleration output signal, and a comparator module connected to the outputs of the gaseous fuel flow control module and the gaseous fuel flow bias module and configured to reduce the adjusted gaseous fuel flow rate by the gas flow bias amount. 
     
     
         29 . The gas substitution control system of  claim 25 , further comprising a comparator configured to compare the output of the non-gaseous fuel flow detector module with a predetermined minimum non-gaseous fuel flow set point, the gaseous fuel flow control module further comprising an integrating module which is programmed to adjust the gaseous fuel flow rate based on the output of the comparator such that the non-gaseous fuel flow is adjusted to be at least substantially equal to the predetermined minimum non-gaseous fuel flow set point, whereby the gas substitution amount is based on the predetermined minimum non-gaseous fuel flow set point. 
     
     
         30 . The gas substitution control system of  claim 29 , further comprising a gaseous fuel flow cut off control module programmed to shut off gaseous fuel flow to the engine if the detected non-gaseous fuel flow is below a predetermined minimum idle non-gaseous fuel flow set point. 
     
     
         31 . The gas substitution control system of  claim 25 , wherein the gaseous fuel flow control module further comprises a data base containing stored calibration data comprising a map of total fuel energy rate versus gas substitution ratios (command GSRs) over a range of engine loads, the gaseous fuel flow control module being programmed to compute a current total fuel energy rate and gas substitution ratio based on current detected gaseous and non-gaseous fuel flow rates, to determine the mapped command GSR corresponding to the current total fuel energy rate, to compare the computed current GSR with the mapped command GSR in order to produce a GSR error, and to vary the gaseous fuel flow based on the current GSR error in order to control the GSR to be at or close to the command GSR corresponding to the current total fuel energy rate. 
     
     
         32 . The gas substitution control system of  claim 25 , wherein the non-gaseous fuel flow injector assembly comprises at least one non-gaseous fuel injector having an injector nozzle communicating with an engine combustion chamber, a non-gaseous fuel flow supply path to at least one non-gaseous fuel flow injector, and a non-gaseous fuel return path from the non-gaseous fuel injector for return of non-gaseous fuel to a fuel tank when non-gaseous fuel is not being injected into the engine combustion chamber, the non-gaseous fuel flow detector module comprising a supply flow meter in the non-gaseous fuel flow supply path for detecting non-gaseous fuel flow to the non-gaseous fuel injector, a non-gaseous fuel return flow meter in the non-gaseous fuel return path, and a comparator module configured to subtract the output of the non-gaseous fuel return flow meter from the output of the fuel supply flow meter to produce a non-gaseous fuel flow output corresponding to the non-gaseous fuel flow input from the at least one non-gaseous fuel injector to the engine combustion chamber. 
     
     
         33 . The gas substitution control system of  claim 25 , wherein the gaseous fuel flow control module is configured to vary gaseous fuel flow to the engine by controlling the gaseous fuel pressure.